Maintenance of certain automotive components such as filter components is typically scheduled on an open-loop basis using mileage or time of use to estimate component wear and need for component replacement. The open-loop estimate of wear as a function of mileage or time of use is typically overinclusive, wherein a worst case wear pattern is assumed to preserve automotive vehicle performance under a majority of cases including cases corresponding to worst case component wear. Overinclusive maintenance scheduling is wasteful in that a significant number of vehicles are scheduled to replace components before the components are actually worn out to the point that vehicle performance may be affected.
Closed-loop maintenance scheduling has therefore resulted for many components of automotive vehicles, in which certain engine operating conditions that affect component wear are logged and component wear estimated as a function thereof. For example, air filter monitoring systems have been proposed in which estimate the increase in restrictiveness of air filters for filtering engine intake air. When the restrictiveness reaches a level that may affect engine or vehicle performance, an air filter maintenance request may be made to the vehicle operator, to initiate manual cleaning or replacement of the air filter.
The proposed air filter monitoring systems require the engine to operate at a level corresponding substantially to a maximum intake airflow. Only under such extreme conditions are the monitoring systems able to diagnose the condition of the air filter. Such operating levels rarely occur for automotive vehicles. It may therefore take a significant amount of time of use or a significant amount of mileage before the proposed monitoring systems can diagnose even a highly restricted intake air filter. The proposed monitoring systems may therefore resolve the problem of overinclusive open-loop maintenance scheduling, but at an unacceptable cost of permitting vehicle operation with highly restrictive intake air filters that may substantially affect vehicle performance.
It would therefore be desirable to accurately diagnose restriction in automotive vehicle intake air filters in a timely manner, such as shortly after the filter becomes restriction, such as by monitoring the restriction level through engine operating conditions that occur with a reasonable frequency.